Maybe they count as a user, but they count comparatively to all the people who don't write him. I'd hardly expect him to get tweets and emails saying "It was so great how your tool printed what I wanted to stdout", even in cases where people do prefer that.
It's tough to get a representative sample from something like voluntary correspondence, because it doesn't tell you the majority opinion, just the majority opinion from people who decided to write in.
EDIT: To note, it's entirely possible that the silent majority of curl users really do hate the default-to-stdout choice. But absent a real way of surveying, it's difficult to make a call either way.
It's tough to get a representative sample from something like voluntary correspondence, because it doesn't tell you the majority opinion, just the majority opinion from people who decided to write in.
EDIT: To note, it's entirely possible that the silent majority of curl users really do hate the default-to-stdout choice. But absent a real way of surveying, it's difficult to make a call either way.